Restricting the receipt API to authenticated users (bug 917601)

Otherwise a 500 will be raised given the usage of `request.amo_user`
missed a possible None in es_app_to_dict
Commit from Mozilla Verbatim by user jasnapaka@jasnapaka.com.: 4945 of 5474 strings translated (5 fuzzy).
add italian (bug 918560)
document ?region in search API (bug 917500)
fix field names in search.rst
Don't apply filters to Collections API when pk/slug/etc lookup is used (bug 915801)
Merge pull request #1163 from diox/collections-dont-filter-lookups

Don't apply filters to Collections API when pk/slug/etc lookup is used (bug 915801)
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5047 of 5474 strings translated (0 fuzzy).
Merge branch 'master' of ssh://github.com/mozilla/zamboni
Commit from Mozilla Verbatim by user mdinic@mozilla.com.: 406 of 5474 strings translated (2 fuzzy).
remove paypal check
Expose fallback used  in Collections API (bug 914318)
Merge pull request #1165 from diox/collections-expose-fallback

Expose fallback used  in Collections API (bug 914318)
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5086 of 5474 strings translated (0 fuzzy).
Merge branch 'master' of ssh://github.com/mozilla/zamboni
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5087 of 5474 strings translated (0 fuzzy).
Commit from Mozilla Verbatim by user petercpg@mail.moztw.org.: 5087 of 5474 strings translated (0 fuzzy).
Removed unused tasks.

See commit af6e6a7896cd9e5aa51d017f2abace084938669e.
check for image presence without database hit (bug 918522)